The Battle Against Leafcutter Ants

Fayette County Agriculture

Leafcutter ants are one of the most difficult pests to eliminate from the landscape. They can strip a mature fruit tree in a day. I have heard them described by my gardening friends as pure evil. But like all critters of the earth, they have a job to do, even if we can’t figure out the job’s value.

One of my unusual friends has an obsession with killing cutter ants. He said he once sat by a cut ant exit hole in a concrete driveway and killed over 15,000 emerging ants in one day. The next day he killed over 10,000. The next day it rained and he didn’t kill any. Soon he decided that he needed a better solution than to waste his day killing ants. So he plugged the hole.

It wasn’t long afterwards that he found another hole. He tried a variety of products and chemicals, from gun powder to gasoline. Some of the chemicals he used are banned around the world, and he still has cutter ants.

A bred leaf cutter queen can lay 1,000 or more eggs a day. She can live for 10 years or more. Once a colony is established, the number of workers can reach well over 7 million. The ants are generally not aggressive, but they can bite if provoked. A single mound can grow to 20 feet by 20 feet by 10 feet deep with multiple exit holes.

Leafcutter ants use leaves and seeds to grow a fungus that they eat. The fungus also supports a small cockroach that lives among the ants. Both fungus and cockroaches board and go with a new queen when she leaves the nest to breed. New queens can number 10 or more a year.

At the family ranch, I generally leave the ants alone. One day while I was driving the tractor down the farm road, my nephew, Michael, decided to speed around me by driving into the pasture. The next thing I knew, his car seemed to disappear. We pulled it out of a three-foot-deep cut ant mound.

Cut ants can form trails that lead to new leaf cutting areas. I have followed the trails and the leaf cutters over 50 yards from their exit hole. It is easy to find them even without a trail. The ant holds the fresh cut leaf high above its head. Strong leafcutters can haul a leaf ten to twenty times their size and weight.

On a client’s ranch, I was asked if I could eliminate several cutter ant mounds in two pastures. The area was about three acres total. The two pastures backed up to a wooded area. The ranch was transitioning to an organically run operation, so I could only use organic solutions. The project started at the end of May.

I began by identifying every exit hole I could find. I put small white flags by each hole. I used up a bundle of 50 flags and added a few more. Every morning after the dew was dried from the grass, I would put about a teaspoon of Red Lake diatomaceous earth into and around each hole. The product is a combination of clay and D.E. Later in the afternoon or early evening, I would come back and put a half teaspoon on any hole that was still in use. Once the hole was dusted, the foraging ants would abandon the leaves at the entrance and wander off to die.

Over a period of three months the number of flags and active holes was reduced to six. Sometimes the ants would build a hole next to the hole I had dusted. Sometimes it was a game of hide and seek as they developed ways of camouflaging the hole. In the fourth month I couldn’t find a leafcutter ant. It took over six months before I noticed a new mound in the area.

I have read that a leafcutter ant can live about 6-10 weeks and can run at speeds over 16 miles per hour. One researcher believes that leafcutter ants prepare the soil for native grasses with the fungus it grows. With over 60 years of observing the ants, I have never witnessed this to be true. Instead, it appears that once native grasses become predominant, the ants leave the area. They seem to prefer an area near trees, but they cut leaves from several plants.

I once tried using essential oils to run off the ants. I tried peppermint, lemongrass oil, rosemary, and a combination of many oils. Most only made the ants create a new exit hole.

One natural product that proved well was Neem oil. I sprayed about 20 gallons of neem oil mix on a 20’ x 20’ mound that was under a large live oak tree. Neem acts as an insecticide and a fungicide. The mound died within a week and did not return for over a year. The new mound was never as active as the original mound.

Amdro Ant Block Granules is a bait product that has a toxic chemical that helps to get rid of some cut ants. I found the bait must be applied every two to three weeks until the mound has completely disappeared from the area. This can take a couple of months to years. However, Amdro also kills beneficial ants.

The one thing that I found that works the best on ridding your landscape of leafcutter ants is persistence. Good luck.

David E. Will is a farmer, rancher, nurseryman, landscaper, and consultant. He can be reached at 830-629-9876 or by email at dwill207@satx. rr.com.